Braun tube



June 4, 1935. K. SCHLESI'NGER- BRAUN TUBE Filed May 15, 1953 PatentedJune 4, 1935 UNITED STATES PATENT OFFICE Application May 13, 1933,Serial No. 670,819

In Germany May 14, 1932 8 Claims.

In the production of Braun tubes and the like the problem frequentlyarises of concentrating or preliminarily concentrating to such extent abundle of electrons (cathode ray), which emerges from a shutteraperture, that after-focusing is rendered possible on full scale, forexample by means of an electron-optical system (for example, inaccordance with the German patent (R. 84 555 VIIIa/2lal)).

According to the invention, there is produced for this purpose, betweenthe outlet aperture for the cathode ray and the point raised to a highpositive potential on to which the ray is to be concentrated, afield,the strength of which diminishes from the outside towards the inside, i.e., towards the outlet aperture for the electrons.

Upon entering a field of this nature there will be acted upon to theleast extent those electrons which move in an axial direction, i. e.,towards the anode, and to the greatest extent those electrons thedirectional angle of which is greatest in relation to the central path,i. e., those electrons which emerge from the outlet aperture at arelatively large lateral angle. In this manner it is possible toconcentrate in preliminary fashion all or at least practically allelectrons emerging from the aperture, to such extent as to ensure properfocusing by means of an after-connected electron-optical system withoutdisturbing effects of a subsidiary kind, such as produced by thoseelectrons which are not brought under the control of the electronopticalsystem.

According to the invention, the concentration field formed pursuant tothe invention may be produced by means of semi-conductors. The inventionmay be more fully understood from the appended drawing, whereof Fig. 1shows schematically the arrangement according to the invention, whilstin Fig. 2 a Braun tube furnished with a circular ring consisting ofsemi-conductive material is shown, and

Fig. 3 is a Braun tube, wherein a semi-conductor is provided whichpossesses the form of a conical tube.

In Fig. 1, l is a shutter having the aperture 2, through which thereemerges the bundle of electrons (electron outlet aperture). The shutterI is preferably constructed in the form of a circular ring, andfurnished with a highly ohmic resistive coating 3 on the side directedtowards the anode. At the outer periphery of the circular ring there isconducted to the resistive coating a suitably selected high negativebias (for example 500-1000 volts), whilst the inner edge at the outletaperture possesses, in comparison potential in relation to the ray, and6 a screening means, the potential of which is selected in such fashionthat the upward point of the field situated between the resistivecoating 3 and the anode l coincides approximately with the centre pointof the anode. Owing to the drop in potential occurring in the resistivecoating along the diameter of the circular ring, it is accomplished thatthe strength of the field decreases from the outside towards the insidein the manner necessary according to the invention.

In Fig. 2 there is shown a suitable form of embodiment of asemi-conductive perforated shutter in conjunction with screeningelectrodes. A stream of electrons passes from a cathode I having arelatively large surface to a metallic shutter 2 without concentration,i. e., with a certain dispersion. The dispersion may certainly alreadybe reduced, preferably by means of a Wehnelt cylinder 9, but it isimpossible with 9 and 2 alone to obtain from a large-surface cathode l asmall focal point on the luminous screen. The arrangement 9, 2 does notcover in lenticularly exact fashion bundles of rays with largedispersion and expanse. The efficiency of the same is greater in thearrangement described in the following.

The potential between 2 and l is positive and relatively small, forexample about +200 volts. The problem resides in focusing of all pathsof electrons on a remotely arranged screen image point 3. This is onlypossible if the. rays of the bundle 4 wandering to the greatest extentare deflected to the greatest degree towards the centre. According tothe invention, this is accomplished by the stated semi-condu'ctiveshutter 5. The inner edge of a disc of mica coated with a resistivesubstance possesses the potential of the screening shutter 2, whilst theouter edge on the other hand is raised to a preferably variable andstrongly negative potential of, say, (-l)-(--500) volts. This ispossible because the shutter possesses a large radial resistance, andtherefore merely a weak current traverses despite the large differencein potential between the inner and the outer edge said current flowingfrom the inner to the outer edge of said electrode. The outer edge ofdisc 5 is supplied with the negative bias through the lead attached tothe lower end of said disc. This lead/is connected to the one pole of asuitable potential source which is not indicated in the drawing, and theother pole of which is connected with the anode 2 which in turn isconnected to the inner edge of the disc 5. Shutters of this nature maybe produced in ready fashion. This actual main anode is the metallicshutter 6, which is furnished with a very small hole. From the edges ofthis hole there proceed to the shutter 5 field lines withconcentricallyv conical inclination having the particularly advantageousproperty that the strength of field on these lines is all the greaterthe more remote the same are from the axis ofthe ray, because their pathintegral, measured in relation to the outer edge of the semiconductiveshutter '5, must be a few hundred volts greater than in relation to theinner edge. Experiments conducted by the applicants have shown that withan arrangement of this kind a very good concentration effect may beobtained, and that in this connection it is possible to suitably adjustthe focus of the system 2, 5, 8 by selection of the potential of theouter edge, and even more that this focus is only varied to aninessential degree upon variation in the first attraction potentialbetween I and 2. The method, therefore, is suitable for use intelevision tubes with light control. Ac-' cording to the' invention,there may also be employed screening walls I. to avoid the effect ofexternal fields, which walls may possess approximately the potential ofthe first anode 2 or the inner edge respectively. It may be accomplishedby a screening means 8, which leaves merely a small ring of the highpotential anode uncovered, that the latter acts virtually with merely avery small opening corresponding with the small reciprocal of 8. Thescreening means are preferably linked up with a potential, whichcorresponds with that of the preliminary anode or that of the inner edgeof the highly ohmic of semi-conductive plate. Naturally the spacingbetween 5 and 8 is open to considerable variation in close connectionwith the potentials employed, and also the radial distribution of thefield may be acted upon systematically by applying the resistivesubstance to the circular shutter 5 not in constant fashion, but incertain fashion to a greater degree on the inside or the outside.

The following arrangement (see Fig. 3) is also on the same basis. Alarge-surface cathode I is situated at the entrance of a conical tube I5. The tube is made from a semi-conductive material, or is coated with amaterial of this nature on the inside and is otherwise insulatory. It ispossible, therefore, to build up between the. closing rings 2 and III ofthis tube a difierence in potential which, with suitable production ofthe tube resistance, may readily amount to a few hundred volts. 'It maythen be observed that a large number of the field lines run parallel tothe walls of the tube, and there is accordingly an excellent possibilityof producing in positive fashion a defined converging acceleration fieldof cylindrically symmetrical kind. A preliminary concentration of thebundle of rays is rendered possible from the largesurface cathode I withthe assistance of a condenser of the Wehnelt cylinder 9 to approximately.50 volts, so that the bundle of rays already enters the metallicshutter 2 with a divergence which is no longer of an excessive kind,

and it is accomplished within the semi-conductor tube I5, the form ofwhich is suitably selected and may even be determined, that theelectrons at the exit of the tube possess components of such naturedirected radially inwards that the same all meet at the one point 3 onthe luminous screen II, Naturally, this electron-optical unit, thesemi-conductor tube I5, may also be combined in many different ways withother arrangements of a known kind. Behind the same, for example, theremay be provided an after-acceleration anode 6 raised to correspondinglyhigher potential, and the like.

Light control may also take place, for example before the entry into theshutter 2, at the Wehnelt cylinder 9, or also otherwise, in the mannerknown per se, without variation in the optical conditions, as the sameare rigidly determined by the semi-conductor tube I5. An advantage ofthe arrangement is also to be regarded in the fact that the opticalaxis, with suitable length of the tube I5, is very well defined,andowing to the large aperture of this optic is not varied even if onaccount of inexact centering of the Wehnelt cylinder 9 upon the lightcontrol small lateral movements of the bundle of rays take place at thecommencement.

The invention is of particular importance for Braun tubes with a hotcathode. The same may be used with advantage in the case of tubes havinga gas filling, but is also of advantage in connection with high-vacuumcathode ray tubes.

of plates, in accordance with the purpose of use, and may also containadditional elements The tubes may naturally be furnished in theknown'manner with one or more pairs.

necessary for particular purposes, and more cathode ray, said meanscomprising an electrode consisting of semi-conductive material, beingarranged between said cathode and said anode.

2. A Braun tube comprising a plate-shaped indirectly heated cathode, ananode, means to control, means to, deflect the cathode ray, afluorescent screen, and a plate-shaped electrode of semi-conductivematerial furnished with an opening, said electrode being arranged in thepath of the cathode ray between said cathode and said anode.

3. A Braun tube comprising a plate-shaped indirectly heated cathode, ananode, means to control, means to deflect the cathode ray, a fluorescentscreen, and a plate of insulating material furnished with an opening andarranged in the path of the cathode "ray between said cathode and saidanode, the side of. said plate of insulating material directed to theanode being coated with a material of a high ohmic resistance, the outeredge of said coating being adapted to be connected with the negativepole, and the'inner edge of said coating being adapted to be connectedwith the positive pole' of a potential source.

4. A Braun tube comprising a plate-shaped indirectly heated cathode, ananode, means to control, means to defiect the cathode ray a fluorescentscreen, a plate-shaped metallic electrode furnished with an openingarranged between said cathode and said anode, a plate-shaped element ofinsulating material furnished on its one side directed to the anodewitha material of a high ohmic resistance, said insulating elementarranged between said metallic electrode and said anode and a furtherplate-shaped metallic electrode furnished with an opening arrangedbetween said semi-conductive element and said anode, said furtherelectrode being connected with the first said one.

5. A Braun tube comprising a plate-shaped indirectly heated cathode, ananode, means to control, means to deflect the cathode ray, a fluorescentscreen, and an electrode of a truncated hollow conical form consistingof poorly conductive material, said electrode arranged between saidcathode and said anode, the end of said electrode directed to the anodeadapted to' have a high positive potential applied thereto.

6. A Braun tube comprising a plate-shaped indirectly heated cathode, ananode, means to control, means to deflect the cathode ray, a fluorescentscreen, and an electrode of a. truncated hollow conical form consistingof poorly conductive material, said electrode arranged between saidcathode and said anode, the end of said electrode directed to the anodebeing adapted to have a high positive potential applied thereto, theconical base of said electrode being directed towards said anode.

'7. A Braun tube comprising a plate-shaped indirectly heated cathode, ananode, means to control, means to deflect the cathode ray and afluorescent screen, a metallic electrode adapted to have a positivepotential applied thereto, arranged between said cathode and said anode,an electrode adapted to have a negative potential applied thereto atleast partly consisting of a material of high ohmic resistance arrangedbetween said electrode and said anode, and a cylinder adapted to have apositive potential applied thereto furnished at its end directed to theanode with a shutter furnished with an opening surrounding said twoelectrodes.

8. A Braun tube comprising a cathode, an anode, a picture receivingscreen, two pairs of deflecting plates for scanning said screen, andmeans for concentrating the cathode ray, said means including anelectrode consisting of semiconductive material, said electrode beingarranged between said cathode and said anode.

KURT SCHLESINGER.

